Allen-Bradley has two versions of the TTL compatible discrete Output modules that will interface to TTL output devices. The 1771-OG module will control eight TTL outputs while the 1771-OGD will control up to 16 outputs. Only the 1771-OG version has a 1ms output filter, while the 1771-OGD version has output diode protection to +5 volts and ground. The TTL voltage ranges are 0 - 0.5V DC for V low, and 2.7 - 5.25V DC for V high. The modules are current rated at I out low, 20mA sink current (the device connected to the module must source no more than this amount), and I out high, 1mA (the module will source this much current).

Remove the module's left hand cover plate (the one without the labels).
Observe the location of the configuration switches in
figure 8.1.
When selecting POSITIVE logic, switch 1 and 2 are set to the ON position.
For NEGATIVE logic, switch 1 and 2 are generally set to the OFF position.

Remove the module's left hand cover plate (the one without the labels).
Observe the location of the configuration switches
figure 8.2
When selecting POSITIVE logic, set strap to the HIGH (right/front) position. For NEGATIVE logic, set strap to the LOW (left/rear) position.

The Allen-Bradley 1771-OG(D) TTL Output Module may be installed in any Allen-Bradley Universal I/O Chassis, 1771-A1B, 1771-A2B, 1771-A3B, or 1771-A4B. Before Installation, calculate the power requirements of the modules currently in the chassis. Add to that 168mA @ 5V DC for the 1771-OG, or 230mA @ 5V DC for the 1771-OGD. Check to be sure that this combined current requirement does not exceed the current driving ability of the chassis power supply.

Only the 1771-OGD module has a fuse to protect the +5V DC power supply and the module's output terminals from the accidental application of voltage that could cause damage, such as voltage over 6.0V DC, reverse DC or AC voltage. Fuse rating: 0.5A at 250V, use Littelfuse 312.250 or similar.

The 1771-OG is not fuse protected so care must be taken to properly connect the power supply. Accidental application of AC, reverse DC, or over voltage could damage the module.

The 1771-0G(D) may be placed in any slot of the I/O chassis with the exception of of the extreme left slot. This slot is occupied by the Remote I/O Adapter Module. It is suggested that analog input modules and low voltage DC modules be placed away from AC modules or high voltage DC modules to minimize electrical noise interference.

The 1771-OGD has an additional restriction. EPICS software reads and writes the Allen-Bradly chassis in Two-slot addressing mode. A module group is considered to contain two Allen-Bradly slots. The first module group address is located at slot 0 and 1. The second is slot 2 and 3 and so on. When using a 16-bit output module in a two-slot addressing mode, the output module must always be inserted into an odd number slot (right-hand side of the module group). A complementary input module (8-bit or 16-bit module) may be inserted into an even number (left-hand side of the module group) slot completing the module group. If no complementary module is used then that slot must remain empty.

The 1771-IG has no such restriction. An 8-bit output module can be used with any 8-bit input or output module. There is no defined order as to which input or output module is inserted in a module group, and two inputs or two outputs can be used in the same module group. However, it is common practice when using an 8-bit output and an 8-bit input module in a module group, to insert the output module into the odd (right-hand) slot and the the input module into the even (left-hand) slot of the module group.

The Allen Bradley Universal I/O chassis have the ability to limit the slot access to certain modules by the implementation of a keying system. Modules are slotted in two places at the edge of the circuit board. The position of the keying bands on the backplane connector of the I/O chassis must correspond to these slots. To key a slot for use by the 1771-OG TTL Output only, place the keying bands between 6 and 8 and between 10 and 12 on the I/O chassis backplane connector. To key a slot for use by the 1771-OGD TTL Output only, place the keying bands between 16 and 18 and between 26 and 28 on the I/O chassis backplane connector.

Before a module is inserted into the Universal I/O Chassis, be sure that the power to the chassis is shut off. This can be done without shutting off the IOC that the Universal I/O Chassis is connected to, and without removing the subnet communication link. To insert the module, place it in the plastic tracks on the top and bottom of the Universal I/O Chassis. Slide the module into the Universal I/O Chassis until the module comes in contact with the backplane connector. Do not force the module in, instead apply firm and even pressure on the module to seat it properly on the backplane connector. Snap the chassis latch over the top of the module and connect the wiring arm to the module. The Universal I/O Chassis should begin communicating with the host IOC when power is reapplied, no rebooting of the IOC will have to be done.

Connecting field wiring to the 1771-OG(D) is accomplished through the use of a shielded cable to the wiring arm. Signals should be connected to the screw terminals on the wiring arm, as detailed in figure 8.3, and the wiring arm should be connected to the front tab connector on the 1771-OG(D). When shielded cable is used and grounding of the shield is desired, it is recommended that the connection be made at one of the I/O chassis mounting bolts. To prevent ground loops only the chassis end of the cable shield should be grounded.

The front panel on the 1771-OG contains nine red LED indicators. The top red LED labeled HIGH-TRUE indicates the module is selected for positive logic when illuminating. The next eight LEDs will indicate if an output is true.

The front panel on the 1771-OGD contains 18 LED indicators. The top green LED labeled ACTIVE indicates the module is connected to +5 volts and the fuse on the 1771-OGD is not blown. The next 16 red LED indicators, labeled 00 through 17 (octal), will indicate if an output is true. The last green LED labeled HIGH indicates the module is selected for positive logic when illuminating.